This invention relates in general to gas testing devices and in particular to a new and useful highly sensitive test tube for determination of gas pollutants.
The advantage of the known test tube method with color indication resides in the possibility of measuring with relatively small test gas volumes (in general 0.5 to 2 liter) the gas pollution in the ppm range (1 ppm=1 cc/m.sup.3). Quantitative measurements at concentrations less than ppm require special expenditures. Generally an increase of the test gas volume is involved. The advantage of the small test gas volume than no longer exists.
A gas dosimeter has become known which has a housing with a backwall and sidewalls. Toward the top it is open. It contains a colorimeter strip sensitive to the gas to be determined and to light. Optionally also a color standard may be arranged for comparison with the colorimeter strip (German No. AS 17 73 339).
A dosimeter tube made according to this design contains in a glass tube a paper strip provided with chemical reagents, which then react with the pollutant to be detected. A color change then occurs. In the state as supplied, the dosimeter tube is fused at both ends. For use it is opened by breaking off a tip at a weakened break line. The ambient air then penetrates into the interior of the tube by diffusion. With progressing diffusion and with the presence of the gas to be detected in the ambient air, the paper strip becomes discolored.
For use in a gas detector, in which a certain quantity of the gas (or air) to be tested is drawn by means of a sampling pump through the test tube for quantitative determination of the pollutant contained, this known dosimeter tube cannot be used. The test air would flow through the tube and hence past the reagent paper strip too fast. Continuous and hence quantitative discoloration of the reagent strip cannot occur because test air would react with the gas to be detected contained in it virtually simultaneously along the entire strip length and hence would discolor.